Re: [PATCH v3] x86/boot: skip realmode init code when running as Xen PV guest

From: Borislav Petkov
Date: Thu Nov 24 2022 - 08:28:26 EST


On Wed, Nov 23, 2022 at 12:45:23PM +0100, Juergen Gross wrote:
> When running as a Xen PV guest there is no need for setting up the
> realmode trampoline, as realmode isn't supported in this environment.
>
> Trying to setup the trampoline has been proven to be problematic in
> some cases, especially when trying to debug early boot problems with
> Xen requiring to keep the EFI boot-services memory mapped (some
> firmware variants seem to claim basically all memory below 1M for boot
> services).
>
> Introduce new x86_platform_ops operations for that purpose, which can
> be set to a nop by the Xen PV specific kernel boot code.
>
> Fixes: 084ee1c641a0 ("x86, realmode: Relocator for realmode code")

This text and Fixes: tag sounds like this needs to go to Linus and
stable now?

> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> index 41d7669a97ad..247aca9f8ed1 100644
> --- a/arch/x86/realmode/init.c
> +++ b/arch/x86/realmode/init.c
> @@ -200,14 +200,18 @@ static void __init set_real_mode_permissions(void)
> set_memory_x((unsigned long) text_start, text_size >> PAGE_SHIFT);
> }
>
> -static int __init init_real_mode(void)
> +void __init init_real_mode(void)
> {
> if (!real_mode_header)
> panic("Real mode trampoline was not allocated");
>
> setup_real_mode();
> set_real_mode_permissions();
> +}
>
> +static int __init call_init_real_mode(void)
> +{
> + x86_platform.realmode_init();
> return 0;
> }
> -early_initcall(init_real_mode);
> +early_initcall(call_init_real_mode);

I'll name that one "do_init_real_mode" as "call init" sounds weird.

Otherwise, it is as straightforward as it gets.

Thx.

--
Regards/Gruss,
Boris.

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